Which way is Greece going to go? Ahead of Sunday's election, with politicians railing from the hustings nationwide, the mood has reached fever pitch. "Euro thriller with all eyes on Athens," proclaimed the mass-selling Ta Nea on Friday, noting: "The entire planet is waiting with bated breath for the results of the Greek vote."

Late into the night and all day, workmen had been assembling a giant stand in Syntagma Square from which Antonis Samaras, the "pro-European" New Democracy leader will address the crowd on Friday evening.

The speech will close a campaign that, although brief, has also been extraordinarily bitter. Greeks are polarised in a way they have never been since the restoration of democracy in 1974. There has never been so much at stake.

If they go to the left and cast their votes in favour of the radical anti-austerity Syriza party, in the capitals of Europe it is unanimously agreed that they will be playing with fire.

If they go to the right and vote in favour of New Democracy they will get more of the old order which got them in the financial mess that has now brought their country to the brink but, so the logic goes, it gives them a bit of time. The conservatives have vowed to renegotiate the arduous fiscal measures demanded in return for rescue loans from the EU and International Monetary Fund but at least they have not pledged to rescind the policies as Syriza's leader, Alexis Tsipras, has done.

Tsipras, who on Friday night gives his finale speech in Salonika, the country's northern capital, has not only threatened to annul the "loan agreement". He insists he can have it both ways: Greece can reject the austerity attached to financial assistance and still stay in the euro. "No to the memorandum of bankruptcy," he told a mass rally Thursday. "Yes to the euro and to a national plan for economic recovery that will protect the people form bankruptcy."

Such pronouncements make European leaders shudder – reject the measures, they say, and there will be no more assistance. And without the loans Greece will default on its debt and be ejected from the single currency.

Greeks are not only divided, they are undecided. Although polls conducted on a private basis for parties have suggested that fear may well have the upper hand – following a discernible shift in support for New Democracy – there is broad consensus that, just as in the inconclusive election on 6 May, voters will make up their minds in the last 48 hours. In the prevailing uncertainty they could still go either way.

With no party expected to win an outright majority, the real question is how effective the new government will be. Apparently Greece will be given 100 days to prove that it can implement the kind of reforms that can put its ramshackle economy back on its feet, according to German officials. Whether it is the left or the right that emerges on top, the new government will be forced to walk a tightrope – with the opposition violently shaking the rope from below.